The present invention relates generally to a family of cellular receptors involved in signal transduction, the seven transmembrane receptors, and more particularly to the cloning and expression of DNA sequences encoding seven novel seven transmembrane receptors.
The seven transmembrane receptors (also known as heptahelical, serpentine, or G protein-coupled receptors) comprise a superfamily of structurally related molecules. Possible relationships among seven transmembrane receptors (7TM receptors )for which amino acid sequence had previously been reported are reviewed in Probst et al., DNA and Cell Biology, 11(1): 1-20 (1992). Briefly, the 7TM receptors exhibit detectable amino acid sequence similarity and all appear to share a number of structural characteristics including: an extracellular amino terminus; seven predominantly hydrophobic xcex1-helical domains (of about 20-30 amino acids) which are believed to span the cell membrane and are referred to as transmembrane domains 1-7; approximately twenty well-conserved amino acids; and a cytoplasmic carboxy terminus. The amino acid similarity among different 7TM receptors ranges from 10% to more than 80% and receptors which recognize similar or identical ligands generally exhibit high levels of homology. The 7TM receptors can be grouped based on their homology levels and/or the ligands they recognize. For example, the interleukin-8 receptor, the angiotensin II receptor, the thrombin receptor, the endothelin receptors, the N-formyl peptide receptor and the C5a receptor all bind peptide ligands and share 20-30% amino acid similarity.
7TM receptors recognize a great diversity of ligands (for example, light, odorants, neurotransmitters, peptide hormones and small molecules) and transduce their signals via heterotrimeric guanine nucleotide-binding proteins (G-proteins) effecting a broad array of biological activities (including visual excitation, olfactory reception, and neurotransmission) through various intracellular enzymes, ion channels and transporters. Signal transduction pathways have been elucidated for rhodopsin [Khorana, J. Biol. Chem., 267: 1-4 (1992) and Stryer, J. Biol. Chem., 266: 10711-10714 (1991)] and the beta-adrenergic receptors [Dohlman et al., Ann. Rev. Biochem., 60: 653-688 (1991)] and are thought to illustrate the pathways utilized by other 7TM receptors. Each 7TM receptor is predicted to associate with a particular G protein at the intracellular surface of the plasma membrane. The binding of the receptor to its ligand is thought to result in activation (i.e., the exchange of (GTP for GDP on the xcex1-subunit) of the G protein which in turn stimulates specific intracellular signal-transducing enzymes and channels. Thus, the function of each 7TM receptor is to discrimnate its specific ligand from the complex extracellular milieu and then to activate G proteins to produce a specific intracellular signal. Cotecchia et al., Proc. Natl. Acad. Sci, USA, 87: 2896-2900 (1990) reports that the intracellular loop of the third transmembrane domain of the 7TM receptors comprises important determinants for receptor coupling to specific G proteins, however, Lefkowitz, Nature, 265: 603-604 (1993) summarizes reports that other regions of 7TM receptors may also be essential in maintaining 7TM receptors in a constrained, inactive conformation until ligand binding occurs.
Recently, several 7TM receptors have been identified which recognize ligands important for immunological and hemostatic activities. Holmes et al., Science, 253: 1278-1280 (1991) describes the interleukin 8 receptor (IL8R1) as involved in neutrophil chemotaxis and Sasaki et al., Nature, 351: 230-233 (1991) reports the angiotensin II receptor (AT2R) is involved in vascular hemostasis. Similarly, the endothelin receptors [Arai et al., Nature, 348: 730-732 (1990)] regulate vasoconstriction and smooth muscle tone. The C5a receptor mediates chemotaxis, granule enzyme release and superoxide generation in vitro and appears to be involved in anaphylaxis and septic shock in vivo [Gerard and Gerard, Nature, 349: 614-617 (1991)]. Thrombin is also recognized by a 7TM receptor and is a potent activator of platelet aggregation, monocyte chemotaxis, lymphocyte mitogenesis and mediates inflammatory responses to vascular injury. The N-formyl peptide (f-met-leu-phe) receptor is responsible for neutrophil chemotaxis and activation [Thomas et al., J. Biol. Chem., 265: 20061 (1990)]. While these 7TM receptors all have peptide ligands, other 7TM receptors that recognize small organic compounds also mediate proinflammatory activities. For example, the Platelet Activating Factor receptor recognizes a bioactive phospholipid [Honda et al., Nature, 349: 342-346 (1991)] which causes platelet aggregation and endotoxic shock. The thromboxane A2 receptor recognizes an arachidonate metabolite which also stimulates vasoconstriction and platelet aggregation and is implicated in stroke and bronchial asthma [Hirata et al., Nature, 349: 617-620 (1991)].
Mutations in the third intracellular loop of one 7TM receptor (the thyrotrin receptor) and in the adjacent sixth transmembrane domain of another 7TM receptor (the luteinizing hormone receptor) have been reported to be the genetic defects responsible for an uncommon form of hyperthyroidism [Parma et al., Nature, 365: 649-451 (1993)] and for familial precocious puberty [Shenker et al., Nature, 365: 652-654 (1993)], respectively. In both cases the mutations result in constitutive activation of the 7TM receptors. Previously, other studies have shown that mutations that prevent the activation of 7TM receptors are responsible for states of hormone resistance which are responsible for diseases such as congenital nephrogenic diabetes insipidus. See Rosenthal et al., J. Biol. Chem., 268: 13030-13033 (1993). Still other studies have shown that several 7TM receptors can function as protooncogenes and be activated by mutational alteration. See, for example, Allen et al., Proc. Natl. Acad. Sci. USA, 88: 11354-11358 (1991) which suggests that spontaneously occuring mutations in some 7TM receptors may alter the normal function of the receptors and result in uncontrolled cell growth associated with human disease states such as neoplasia and atherosclerosis. Therefore, mutations in 7TM receptors may underlie a number of human pathologies.
Because a variety of therapeutic uses may be projected for 7TM receptors involved in immunological processes in both health and disease states and because it is generally believed that numerous proteins are involved in immunological processes, there continues to exist a need in the art for the identification of additional 7TM receptors that participate in such processes and especially a need for information specifically identifying and characterizing such proteins in terms of their amino acid sequence. Isolation of DNA encoding a novel 7TM receptor also provides the basis for determination of the role of receptor in health and disease states. To the extent that such receptors might form the basis for the development of therapeutic and/or diagnostic agents, it is essential that the DNA encoding them be isolated. The isolated DNA would, for example, provide for the large scale production of the 7TM proteins, allow for the identification of cells naturally producing them, and permit the preparation/identification of antibody substances and/or other novel binding substances (including natural ligands, agonists and antagonists) which are specifically reactive with a particular 7TM receptor (or group of receptors) and which have the capacity to modulate the biological activities of the receptor(s).
The present invention provides purified and isolated polynucleotides (i.e., DNA sequences and RNA transcripts thereof) encoding seven novel 7TM rectors designated V28, V31, V112, R20, R2, R12, and RM3 as well as polypeptide variants (including fragments and analogs) thereof which possess at least one ligand/receptor binding activity or immunological property specific to one of the seven 7TM receptors. Fragments of a 7TM receptor of the invention which correspond to the N-terminal extracellular domain; the transmembrane domains; the individual extracellular and intracellular loops connecting the transmembrane domains; the C-terminal cytoplasmic domain and fusions thereof are specifically contemplated. Preferred DNA sequences of the invention include genomic and cDNA sequences as well as wholly or partially chemically synthesized DNA sequences.
Specifically illustrating polynucleotide sequences of the present invention are the DNA inserts encoding the V28, V31, V112, R2, R12 and R20 7TM receptors in plasmids which were deposited with the American Type Culture Collection (ATCC), 12301 Parklawn Drive, Rockville, Md. 20852, on Oct. 12, 1992 and were respectively assigned ATCC Accession Nos. 75330, 75327, 75326, 75329, 75331 and 75328. Also illustrating polynucleotide sequences of the invention is the DNA insert encoding the RM3 7TM receptor in a plasmid which was deposited with the ATCC on Nov. 2, 1992 and was assigned ATCC Accession No. 75340.
According to another aspect of the invention, biologically active plasmid and viral DNA vectors incorporatng DNA sequences of the invention are provided as well as vectors wherein the DNA encoding a 7TM receptor or 7TM receptor variant is operatively linked to an endogenous or heterologous expression control sequence. Also provided by the invention are procaryotic or eucaryotic host cells stably transformed or transfected with a DNA sequence of the invention so that the 7TM receptor polypeptide or variant polypeptide encoded by the DNA sequence is expressed in the host cell. Host cells expressing such 7TM products can serve a variety of purposes. To the extent that the expressed products are xe2x80x9cdisplayedxe2x80x9d on host cell surfaces, the cells may constitute a valuable immunogen for the development of antibody substances specifically immunoreative with 7TM receptors or 7TM recptor variants. Host cells of the invention are conspicuously useful in methods for the large scale production of 7TM receptors when the cells are grown in a suitable culture medium and the 7TM receptor polypeptide products are isolated from the cells or from the medium in which the cells are grown. Host cells expressing the novel 7TM receptors are also useful in assays for identifying antagonists or agonists of 7TM receptor binding.
Novel 7TM receptors of the invention may be obtained as isolates from natural cell sources, but are preferably produced by recombinant procedures involving host cells of the invention. The products may be obtained in fully or partially glycosylated, partially or wholly de-glycosylated, or non-glycosylated forms, depending on the host cell selected for recombinant production and/or post-isolation processing. 7TM receptor variants of the invention may comprise water soluble and insoluble polypeptide or peptide fragments, and may also comprise polypeptide analogs wherein one or more of the naturally specified amino acids is deleted or replaced: (1) without loss, and preferably with enhancement, of one or more biological activities or immunological characteristics specific for the 7TM receptor; or (2) with specific disablement of a particular ligand/receptor binding function. Analog polypeptides including additional amino acid (e.g., lysine) residues that facilitate multimer formation are contemplated.
Also comprehended by the present invention are antibody substances (e.g., monoclonal and polyclonal antibodies, single chain antibodies, chimeric antibodies, CDR-grafted antibodies and the like) or other binding proteins which are specifically reactive with 7TM receptor or 7TM receptor variants of the invention. Antibody substances can be developed using isolated natural or recombinant 7TM receptor products (including peptides) or cells expressing such products on their surfaces. The antibody substances are useful, in turn, in complexes for immunization to generate anti-idiotypic antibodies as well as for purifying polypeptides of the invention and for identifying cells producing the polypeptides on their surfaces. Assays for the detection and quantification of 7TM receptors on cell surfaces and in fluids such a serum may involve a single antibody substance or multiple antibody substances in a xe2x80x9csandwichxe2x80x9d assay format. The antibody substances as well as agonists or antagonists of 7TM receptor binding (e.g., small molecules or peptides) are also manifestly useful in modulating (i.e., blocking, inhibiting or stimulating) ligand/receptor binding reactions of 7TM receptors of the invention, especially those reactions involved in immunological and/or inflammatory events in vivo.
The scientific value of the information contributed through the disclosures of DNA and amino acid sequences of the present invention is manifest. As one series of examples, knowledge of the sequence of a cDNA for a 7TM receptor makes possible the isolation by DNA/DNA hybridization of genomic DNA sequences encoding the 7TM receptor and specifying the 7TM receptor gene expression control regulatory sequences such as promoters, operators and the like. DNA/DNA hybridization procedures carried out with DNA sequences of the invention and under stringent conditions are likewise expected to allow the identification of DNAs encoding allelic variants of a 7TM receptor, mutant forms of a 7TM receptor associated with a particular disease state, other structurally related proteins sharing the biological and/or immunological specificity of the 7TM receptor, and non-human species proteins homologous to the 7TM receptor. DNAs of the invention are useful in DNA/RNA hybridization assays to detect the capacity of cells to synthesize a 7TM receptor.
Also made available by the provision of DNA sequences of the invention are therapeutically useful oligonucleotides (e.g., antisense oligonucleotides, oligonucleotides for triplex formation or aptamers) relevant to regulating expression of a 7TM receptor by those cells which ordinarily express the same [as is described for other oligonucleotides in Crooke et al., BIO/TECHNOLOGY, 10: 882-886 (1992) and in Alper, BIO/TECHNOLOGY, 11: 1225 (1993)]. DNA sequences of the invention may also be used in vectors which have been developed for gene therapy such as those described in Mitani et al., TIBECH, 11: 162-166 (1993) (delivering therapeutic genes); Sikora, TIBTECH, 11: 197-201 (1993) (gene therapy for cancer); and Findeis et al., TIBTECH, 11: 202-205 (1993) (gene therapy via receptors).
Numerous aspects and advantages of the present invention will be apparent upon consideration of the following drawings and detailed description.